A proposed solution to the problem of transfusion-associated viral hepatitis is the use of saline-washed packed red cells as the usual form of blood replacement. The present study seeks to determine whether the most widely used technique of washing red cells actually achieves a significant reduction in the incidence of transfusion-associated infections. Its method is a prospective comparison of risk among patients receiving only washed erythrocytes, those given unprocessed units, and untransfused patients undergoing open-heart surgery. An additional goal is documentation of the efficiency of the technique used so that either a positive or negative result can be related to the amount of dilution achieved. Units of blood are experimentally contaminated with various markers detectable in trace amounts, and the procedure varied to determine the shape of the dilutional curve under different conditions.